The fact that a Ga2-xFexO3 crystal has magneto-electric properties has been described by Yu. F. Popov et al., in [JETP 87(1), 146(1998)], and in recent years, this material has drawn attention as a first material having polarization as well as ferromagnetism.
However, since the crystal size of a Ga2-xFexO3 crystal which can be manufactured by a conventional manufacturing method has been too small, approximately 1 mm in diameter, to be used in practice, of course, the crystal has not been used in practice, and furthermore, the properties thereof have not been evaluated as of today.
The conventional manufacturing method of a Ga2-xFexO3 crystal is a crystal formation method in accordance with a flux method [I. S. Jacos; Journal of Applied Physics; Vol. 31, No. 5 263S (1960)].
According to this method, a crystal is obtained by the steps of mixing appropriate amounts of Ga2O3, Fe2O3, B2O3, and Bi2O3; holding a liquid melted in B2O3 and Bi2O3 at 1,125° C. for five hours; and then performing slow cooling at a rate of 4 to 7° C./Hr. The crystal obtained by this method is a small crystal having a diameter of approximately 1 mm [Elizabeth A. Wood; Acta Cryst. 13, 682 (1960)].
In accordance with the flux method described by I. S. Jacos, the inventors could obtain a crystal; however, the crystal thus obtained was small as described above, and a crystal having a diameter of up to several millimeters could not be obtained. In addition, it was also found that there have been the following problems. That is, in the above manufacturing method of a Ga2-xFexO3 crystal, a targeted Fe composition (X) of Ga2-xFexO3 is generally determined by a mixing ratio between Ga2O3 and Fe2O3, which are used as starting materials.
However, the actual Fe composition (x) of a fine crystal obtained by the flux method described above was different from an expected composition. That is, according to an inductively coupled plasma (ICP) analytical result, it was found that, although a targeted mixing ratio x was 1.08, x of the composition actually obtained was 1.12. Since the difference in composition thus described has a significant influence on a temperature Tc at which the transition to ferrimagnetism occurs (see FIG. 8), the fact that a targeted Tc cannot be controlled is a serious problem.
In addition, variation in composition among a plurality of Ga2-xFexO3 crystals formed by a flux method may occur at high probability, and as a result, a problem may arise when Tc's of a plurality of crystal grains thus formed are controlled.
Furthermore, according to the result of X-ray analysis, a plurality of diffraction lines was observed in a sample which was believed to be one crystal, and hence it was confirmed that the crystal described above is liable to have a twin structure. For a Ga2-xFexO3 crystal having strong magnetic anisotropy, this twin structure is a fatal disadvantage.
By the reasons described above, the Ga2-xFexO3 crystal formed by a flux method was not only small but was also hardly used for industrial applications in view of the crystal quality thereof.